1. Field of the Invention
The present invention relates to a device having a high-quality dielectric thin film, and more specifically, to a thin film capacitor which can be highly integrated, an ultrasonic-wave/electric-signal transducer capable of handling ultrasonic waves of megahertz order or higher, or an optical device having excellent characteristics.
2. Description of the Related Art
Dielectric materials such as lead zirconate titanate (PZT: PbZr.sub.1-x Ti.sub.x O.sub.3), and strontium titanate (SrTiO.sub.3), are shaped into thin films, and used as various types of device.
PZT, in particular, is known as a typical ferroelectric material, and PZT thin films are formed on various types of substrates to manufacture ferroelectric device. In practice, MgO singlecrystalline type, silicon singlecrystalline type, and platinum type substrates are generally used. As for making thin films, physical vapor deposition (PVD) methods such as sol-gel, sputtering, vapor deposition, and laser abrasion methods, or chemical vapor deposition (CVD) methods are used. However, PZT thin films prepared by these methods are mostly of the non-orientational, or polycrystalline type. With the conventional methods, singlecrystalline thin films without defects have not been manufactured.
It is known that a singlecrystalline PZT thin film contributes to improvement of the dielectricity and remanence, and reduction of the leak current. In other words, with a PZT singlecrystalline thin film, the characteristics of various types of ferroelectric devices can be improved.
A specific example of the dielectric device is a thin film capacitor, and the performance of this device greatly depends upon the characteristics of the dielectric thin film.
However, a conventional thin film capacitor entails a drawback, namely, a large leak current due to deterioration of the characteristics of dielectric thin films located close to an electrode. Further, in order to increase the capacitance of a capacitor, the thickness of a dielectric thin film used for the capacitor is reduced; however, if the film is made too thin, the performance of the capacitor deteriorates.
The performance of a capacitor, which so much depends on the characteristics of the dielectric thin film, is an important factor of a memory cell such as DRAM. A conventional DRAM capacitor, which has a structure in which a dielectric film made of silicon oxide (SiO.sub.2), silicon nitride (Si.sub.3 N.sub.4), or the like, is formed on a lower electrode, is not still a satisfactory product in terms of degree of integration, capacitance, etc.
Lately, the above-described PZT has been proposed as a dielectric material in place of silicon oxide, or the like. Further, tantalic oxide (Ta.sub.2 O.sub.5), strontium titanate (SrTiO.sub.3), and barium titanate (BaTiO.sub.3) are dielectric materials which exhibit characteristics similar to those of PZT, and can be used as dielectric thin films of capacitors. However, with any of the conventional film thinning methods, dielectric thin films having excellent characteristics have not been obtained from the above-mentioned dielectric substances. Such a trial raises a drawback similar to the case of the thin film capacitor, more specifically, even if the thickness of the dielectric thin film is reduced, a charge capacitance large enough and leak current low enough to be used as a capacitor of a DRAM cannot be achieved.
As described above, the performance of a device having a dielectric thin film can be improved by upgrading the characteristics of the dielectric thin film. However, such a high performance device has not yet been achieved.